Refractive index control optical semiconductor device

Abstract

A refractive index control optical semiconductor device includes a semiconductor p-n junction structure, and a refractive index control semiconductor layer. The semiconductor p-n junction structure outputs light with a forward current. The refractive index control semiconductor layer is formed on a semiconductor substrate, is stacked on the semiconductor p-n junction structure to constitute an optical waveguide, causes a refractive index change of light to occur by carrier injection, and includes a multi-quantum well structure formed by alternately stacking a semiconductor quantum well layer and a barrier layer having a bandgap larger than that of the semiconductor quantum well layer at a plurality of periods. The semiconductor quantum well layer has a lattice constant smaller than that of the semiconductor substrate. The thickness of the semiconductor quantum well layer is set such that a lowest heavy hole sub-band and a lowest light hole sub-band of the semiconductor quantum well layer have nearly the same energy at a Γ-point in a wave number space.

What is claimed is: 
     
       1. A refractive index control optical semiconductor device comprising: a semiconductor p-n junction structure for outputting light with a forward current; and   a refractive index control semiconductor layer which is formed on a semiconductor substrate, is stacked on said semiconductor p-n junction structure to constitute an optical waveguide, causes a change of refractive index of light to occur by carrier injection, and includes a multi-quantum well structure formed by alternately stacking a semiconductor quantum well layer and a barrier layer having a bandgap larger than that of said semiconductor quantum well layer at a plurality of periods, said semiconductor quantum well layer having a lattice constant smaller than that of said semiconductor substrate, and a thickness of said semiconductor quantum well layer being set such that a lowest heavy hole sub-band and a lowest light hole sub-band of said semiconductor quantum well layer have nearly the same energy at a Γ-point in a wave number space.   
     
     
       2. A device according to claim 1, wherein said semiconductor quantum well layer has a thickness of 4.3 nm. 
     
     
       3. A device according to claim 1, wherein said multi-quantum well structure is constituted by stacking said semiconductor quantum well layer and said barrier layer at seven periods. 
     
     
       4. A device according to claim 1, wherein said semiconductor p-n junction structure has a mesa-shaped double heterostructure in which an active layer is vertical sandwiched by cladding layers to output a laser beam and comprises a diffraction grating formed on a facet of said optical waveguide in a laser resonance direction to select an oscillation wavelength, and said refractive index control optical semiconductor device is a tunable semiconductor laser in which an optical pitch of said diffraction grating changes due to a refractive index change of said refractive index control semiconductor layer serving as a wavelength tuning layer to change a laser oscillation wavelength. 
     
     
       5. A refractive index control optical semiconductor structure comprising a refractive index control semiconductor layer which is formed on a semiconductor substrate to constitute part of an optical waveguide, causes a change of refractive index of light to occur by carrier injection, and includes a multi-quantum well structure formed by alternately stacking a semiconductor quantum well layer and a barrier layer having a bandgap larger than that of said semiconductor quantum well layer at a plurality of periods, said semiconductor quantum well layer having a lattice constant smaller than that of said semiconductor substrate, and a thickness of said semiconductor quantum well layer being set such that a lowest heavy hole sub-band and a lowest light hole sub-band of said semiconductor quantum well layer have nearly the same energy at a Γ-point in a wave number space.